Plasma-induced discharge electrolysis using cathodic discharge is one practically available method for producing fine metal particles. In this method, metallic ions are dissolved in molten salt electrolyte to be reduced by the discharge electrons emitted from the cathode, to produce metal particles in the molten salt electrolyte.
This method uses molten salt electrolyte containing metallic ions. For example, a production method of fine metal particles using plasma-induced cathodic discharge electrolysis is described in WO 2005/111272 (Patent Document 1), for which the desired metallic ions are supplied by dissolving such metal nanoparticle sources as the metal oxide of the corresponding element for the desired metal nanoparticle in the molten salt electrolyte. It also describes to place an anode in molten salt electrolyte, which consists of the corresponding element for the desired metal nanoparticle, to provide with metallic ions for the molten salt by electrochemical anodic dissolution of the anode in the molten salt electrolyte.
H. Kawamura, K. Moritani, and Y. Ito, Plasmas & Ions, 1, 29-36 (1998) (Non-Patent Document 1) describes the production method of fine silver particles using plasma-induced cathodic discharge electrolysis. For supplying silver ions in the molten salt electrolyte, silver chloride as the halide containing the silver element was added and chemically dissolved in the electrolyte.
On the other hand, Japanese Unexamined Patent Application Publication No. 2007-16293 (Patent Document 2) describes how the metal is deposited on the cathode by electrochemical reduction of the metal oxide powders that contact the surface of the cathode immersed in molten salt electrolyte in which metal oxide powders are suspended.